Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, and particularly, is suitable for image pickup optical systems of image pickup apparatuses, such as a digital still camera, a film camera and a video camera.
Description of the Related Art
In recent years, a zoom lens that has a wide angle of view, a small size and a high aperture ratio has been demanded as an image pickup optical system used for an image pickup apparatus.
A negative-lead type zoom lens where a lens unit having a negative refractive power is disposed nearest to the object side has been known as a zoom lens that is small in size over the entire system and has a wide angle of view and a high aperture ratio. Japanese Patent Application Laid-Open No. 2009-282466 and Japanese Patent Application Laid-Open No. 2011-81185 disclose, as a negative-lead type zoom lens, a three-unit zoom lens that includes, in order from an object side to an image side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; and a third lens unit having a positive refractive power.
The negative-lead type three-unit zoom lens including the three lens units described above is advantageous in increase in angle of view and in reduction in size over the entire system. Unfortunately, the entire lens system is asymmetric, which increases variation in various aberrations during zooming. It is thus difficult to obtain high optical characteristics over the entire zoom range.
For achieving high optical characteristics over the entire screen over the entire zoom range while reducing the size over the entire system in a negative-lead type three-unit zoom lens, it is important to appropriately set the refractive power and the lens configuration of each lens unit, and the amount of movement during zooming. For example, to reduce the entire length with the lens retracting, a lens configuration is important that can favorably correct various aberrations while reducing the number of component lenses in each lens unit.
Typically, in a negative-lead type zoom lens, the incident heights of axial rays are highest at the second lens unit over the entire zoom range. Consequently, various aberrations are strong in the second lens unit. For achieving a high aperture ratio and high image quality in a negative-lead type zoom lens, it is important to appropriately set the lens configuration of the second lens unit.